1. Field of the Invention
The present invention relates to a trackball used for controlling electronic devices and an in-vehicle device controller using the trackball. More particularly, the present invention relates to a trackball which is capable of providing the user with a feel of rotating a ball included in the trackball and to an in-vehicle device controller using such a trackball.
2. Description of the Background Art
A trackball is a device used for controlling electronic devices by rotating a ball included in the trackball.
In cases where a trackball is used to operate a personal computer, it is desirable for the pointer on the PC screen to be able to make minute movements in response to movement of the trackball's ball. Thus, it is preferable that a ball included in such a trackball rotate smoothly without interruption of movement while rotating and without giving the user an awkward feel.
On the other hand, in cases where a trackball is used to control the set temperature, etc., in an air-conditioning system, the cursor on a control screen only needs to be able to move in a stepwise manner, and there is no need for the cursor to move smoothly. Therefore, it is preferable that a ball included in such a trackball rotate intermittently in a manner such that the ball rests stably once at a stage where the ball has rotated a predetermined angle to give the user a resistance feel and then again begins rotating as the user applies further force. The feel given to the user when the ball makes such a movement is hereinbelow called a crisp click. The user can, by obtaining a crisp click, intuitively adjust a set temperature, etc., and can obtain a good operational feel.
Conventionally, trackballs that provide a crisp click have been suggested (see Japanese Laid-Open Patent Publication No. 2002-140160).
FIG. 20 is a cross-sectional view of a conventional trackball 200 that provides a crisp click. In FIG. 20, the trackball 200 includes a ball 221, a case 222, four fixed magnetic members 231 to 234 (note that the magnetic members 232 and 234 extend in a direction perpendicular to the plane of FIG. 20 and thus are shown by a dotted line in FIG. 20), and magnetic sensors 236A, 236B, 237A, and 237B (note that the magnetic sensor 237B is present at the far end along a direction perpendicular to the plane of FIG. 20 and thus reference numeral 237B is shown in parentheses in FIG. 20).
The ball 221 has included therein three bar members 226, 227, and 228 arranged on three axes that intersect with one another at the center of the ball 221 and are orthogonal to one another. The bar members 226, 227, and 228 are made of an unmagnetized magnetic material, such as iron, and are embedded inside the ball 221.
The case 222 is used to rotatably support the ball 221. The fixed magnetic members 231 to 234 are disposed on the inner surface of the case 222 on two axes orthogonal to each other on a horizontal plane penetrating through the center of the ball 221, so as not to contact with the ball 221.
The magnetic sensors 236A and 236B are provided to detect a rotation of the ball 221 in the longitudinal direction. The magnetic sensors 237A and 237B are provided to detect a rotation of the ball 221 in the transverse direction.
Among the three bar members 226, 227, and 228 embedded in the ball 221, any two bar members present on the same plane are attracted by the magnetic force of the fixed magnetic members 231 to 234. Therefore, for example, in a state shown in FIG. 20, by the force with which the fixed magnetic members 231 and 233 attract the bar member 226, a magnetic-force-based rotation axis emerges between the fixed magnetic members 231 and 233. In addition, by the force with which the fixed magnetic members 232 and 234 attract the bar member 227, a magnetic-force-based rotation axis emerges between the fixed magnetic members 232 and 234. Thus, the user can rotate the ball 221 around either of these axes.
For example, when a force is applied to the ball 221 in a Y direction (see the arrow in FIG. 20), the ball 221 rotates around the rotation axis connecting between the fixed magnetic members 232 and 234. Here, since the bar member 226 is attracted to the fixed magnetic members 231 and 233, the user feels the magnetic force of the fixed magnetic members 231 and 233 while applying a force to the ball 221. As the rotation of the ball 221 proceeds, the bar member 228 is attracted to the fixed magnetic members 231 and 233. When the ball 221 has been rotated by 90°, the bar member 228 is attracted to the fixed magnetic members 231 and 233. Consequently, the ball 221 stops stably. If the ball 221 is further allowed to rotate, the user would feel the magnetic force acting between the bar member 228 and the fixed magnetic members 231 and 233, as a resistance. Accordingly, the user can feel that the ball 221 rotates without play, and can obtain a crisp click every 90° rotation.
In the above-described conventional trackball, however, by the force that the user applies to the ball, the distance between the ball and the fixed magnetic members changes slightly. This causes a great change in the magnetic coupling between the ball and the fixed magnetic members. Hence, when the ball is allowed to rotate, the force of the bar members embedded in the ball and the fixed magnetic members fixed to the case wanting to come into contact with one another acts strongly. As a result, an operational feel given to the user is not always satisfactory.